1. Field of the Invention
This invention relates to a novel process for the preparation of heterocyclic phosphorus compounds and is more particularly concerned with the preparation of 1-aliphatically substituted-2 or 3-phospholene-1-oxides and 1-sulfides.
2. Description of the Prior Art
U.S. Pat. No. 2,663,737 describes the preparation of 1-hydrocarbyl-substituted phospholene oxides by condensing butadiene, or a substituted butadiene, with the appropriate dihalohydrocarbylphosphine and hydrolyzing the intermediate 1,1-dihalo-1-hydrocarbylphospholene by adding water to the reaction product.
U.S. Pat. No. 2,663,738 describes the preparation of the corresponding 1-hydrocarbyl-substituted phospholene sulfides by an analogous method.
U.S. Pat. No. 2,853,473 describes the use of the 1-hydrocarbyl-substituted phospholene 1-oxides and 1-sulfides so obtained as catalysts for the conversion of isocyanates to carbodiimides.
Vizel et al., J. Gen. Chem. (USSR), 43, No. 10, 2137 - 2143, 1973, show an Arbuzov reaction in which a 1-hydrocarbyloxyphospholene is reacted with an alkyl halide and the alkyl of the latter is shown as becoming attached to phosphorus. In our experience no such reaction takes place.
Commercial demand for the above phospholene derivatives has recently increased due to the usefulness of these compounds in the preparation of polymeric foams containing carbodiimide linkages, which latter foams are finding increasing use as insulating materials characterized by thermal stability, low flame spread ratings and low levels of smoke generated under fire conditions.
It is an object of this invention to provide improved methods for the preparation of the above phospholene derivatives. In particular, it is an object of this invention to provide methods which reduce significantly the cost of production of the above phospholene derivatives. Since the cost of the phospholene derivatives is a relatively large proportion of the total cost of preparing polymeric foams containing carbodiimide linkages, such a reduction in manufacturing costs for the phospholene derivatives necessarily gives rise to a corresponding reduction in the cost of preparing the polymer foams.
Other advantages in the development of the novel process of the invention will become apparent from the description which follows.